A Time to Digital Converter (TDC) may be considered as a very high precision counter/timer that can record the time of an event to sub 1 ns resolution. The TDC may be used to measure the time of flight of a photon from a laser pulse to a target and back to a photo sensor. The digital time, provided by the TDC, is used as an address to access a corresponding memory location. Each memory location corresponds to a time period equal to the least significant bit of the TDC. This memory location is then incremented. Multiple measurements will result in the building up a histogram in memory. Histogramming readout technique traditionally involves periodically streaming all the readout contents from memory to a computer. The computer would then analyse the data to determine the position of a peak. To determine the range, the computer selected the region of interest (peak region) and carried out a Gaussian fit to determine the true peak. This technique is extremely time consuming requiring the streaming of large amounts of data and then implementing a complex calculation. In a fast application the time taken using this technique is not acceptable.
There is therefore a need to provide for a histogram readout method and circuit for determining the time of flight of a photon which addresses at least some of the drawbacks of the prior art.